This invention relates generally to hermetic refrigeration compressors and, more particularly, to discharge valves for relatively small size refrigeration compressors of the type used in household appliances.
Hermetic refrigeration compressors are used in a large number of household appliances, such as refrigerators and food freezers. Most of these compressors use a single reciprocating piston operating on a horizontal axis and driven by a relatively high-speed, two-pole, electric motor at a nominal 3600 r.p.m. The cylinder in which the piston reciprocates has a cylinder head incorporating intake and discharge valves, and these valves are almost universally of the reed-type using a flat strip of springlike material to close off the intake or discharge port. Normally, these compressors use a single valve plate having a suction valve located on the piston side of the valve plate and a discharge valve located on the outer side of the valve plate in a discharge plenum chamber, which in turn is connected to the discharge line through a muffler arrangement.
The suction and discharge valves operate under different conditions, and therefore are generally quite different in construction. The suction valve operates at a relatively low pressure differential, i.e., the pressure existing within the sealed case of the compressor which is connected to the return line of the system and that pressure within the cylinder when the piston is on the suction stroke. Since the case pressure is relatively low, the pressure differential across the suction valve is also relatively low, and for proper efficiency, the suction port is generally relatively large in diameter, and therefore requires that the reed valve have a relatively large sealing surface. However, the suction valve is able to remain open over a substantial length of the suction stroke, and generally will not close until after the piston has gone through the bottom reversal and begun the compression stroke, and the increasing pressure inside the cylinder as the compression stroke begins assists the spring action of the reed in the suction valve to aid in the closing action. Thus, in general, suction valves tend to be much larger and generally use a cantilever-type construction for the reed.
On the otherhand, the discharge valve operates under quite different conditions. Except during initial start-up conditions, the pressure in the discharge plenum will be relatively high under steady-state operation conditions, and the discharge valve will not and cannot open until the pressure within the pumping cylinder exceeds the discharge pressure and the biasing force holding the discharge valve in a closed position. Thus, the discharge valve will not open until the piston has completed a substantial portion of its compression stroke, and after the piston reaches the end of the compression stroke, the discharge valve must close very quickly as the motion of the piston reverses to prevent high-pressure gases in the discharge plenun from flowing back into the cylinder, a condition which can result in a substantial drop in the efficiency of the compressor. These conditions generally require that the discharge valves be relatively low in mass and operate through a relatively short range of movement; therefore, the design of the compressor discharge valve tends to become rather complex and a large number of designs have evolved to meet the varying conditions of different compressors.
One such design is shown in the patent of R. W. Doeg, U.S. Pat. No. 2,970,608, which utilizes a rigid stop member resiliently secured to the outside of the valve plate and a single valve reed which is secured to the posts mounting the stop member and movable to and from the valve plate which has a pair of discharge points arranged symmetrically with respect to the transverse centerline of the stop member and the mounting posts. This design has been used quite successfully in larger size refrigerator compressors in the 1/4 to 1/3 horsepower range, but efforts have been made to further improve the efficiency of the discharge valve in smaller compressors operating in the range of 1/6 or 1/5 horsepower. One such design is shown in the patent of R. W. Doeg, U.S. Pat. No. 3,039,487, which utilizes a mounting arrangement somewhat similar to that disclosed in U.S. Pat. No. 2,970,608 except that in place of the single valve reed it utilizes three separate members including two reeds operating back-to-back and a stiffer flexible stop member. With this valve, a high degree of efficiency is obtained in smaller compressors because of the two-stage action of the valve, in which, under initial pull-down conditions when the pressure in the discharge plenum is low, the high volume of gas will be discharged starting at the beginning of the compression stroke and the flexible stop is allowed to deflect to give increased travel for the valve reed to provide a higher opening at the discharge port. This larger travel still allows relatively prompt closing of the valve, since only the closure reed must move back against the valve plate as the piston reverses. When the pressure in the discharge plenum increases, as occurs under normal running conditions, the valve reed need not open as far and will not begin to open until the piston is moved farther along on the compression stroke. In this case, because of the higher pressure in the discharge plenum, the volume of gases to be discharged through the discharge valve will be relatively lower because of the increased pressure, and in such case the valve reed moves through a shorter distance and the flexible stop member will tend to deflect very little, if at all, during operation. Although the valve shown in U.S. Pat. No. 3,039,487 is disclosed as sealing against a pair of discharge ports, with a symmetrical arrangement with respect to the mounting pins, it has been found that such valve works equally well if one of the two discharge ports is eliminated and the other discharge port increased slightly in diameter while remaining in the same location as shown in the patent.